Simultaneous Dual-Band Image Sensors

ABSTRACT

A simultaneous dual-band image sensor having a plurality of pixels includes a substrate, a common ground on the substrate, wherein each pixel includes a Band  1  absorber layer on the common ground layer, a barrier layer on the Band  1  absorber layer, a Band  2  absorber layer on the barrier layer, a ring opening in the pixel formed by a removed portion of the Band  2  absorber layer, a removed portion of the barrier layer and a removed portion of the Band  1  absorber layer, wherein the ring opening does not extend through the Band  1  absorber layer, a first contact on a portion of the Band  2  absorber layer inside the ring, and a second contact on a portion of the Band  2  absorber layer outside the ring. The Band  1  absorber layer and the Band  2  absorber layer are n-type, or the Band  1  absorber layer and the Band  2  absorber layer are p-type.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to and claims priority from U.S. ProvisionalApplication Ser. No. 62/832,693, filed Apr. 11, 2019, which isincorporated herein as though set forth in full.

STATEMENT REGARDING FEDERAL FUNDING

None

TECHNICAL FIELD

This disclosure relates to dual-band and two-color image sensors.

BACKGROUND

Some prior art dual-band sensors operate in a sequential mode with oneband sensed and then another band sensed, which results in a blindmoment for each band when the other band is being sensed. Other priorart dual band sensors operate in a simultaneous mode; however, theirfabrication process is complicated, has low yield and is difficult toscale up for reduced pitch size, or increased format size. Most of theprior art approaches need either a diffusion/implantation step or ametal bridge from a middle layer to a top layer. Both these steps addcomplexity in the fabrication process. Further, none of prior art claimsto work for unipolar two-color designs (nBn or pBp) with thin barrierlayers. Unipolar detector designs have shown many advantages overtraditional photodiode detectors and in recent years are preferred forsingle-color and sequential mode two-color image sensors.

Generally, image sensors need to be connected to a separate signalprocessing component. A hybridization bump or interconnect approach hasbeen used to form electrical connection, so that each sensing element(pixel) mates to a signal processing counterpart. The bump may be anindium (In) bump, and the interconnect approach may be a metalinterconnect.

For single-color sensors, or two-color sensors operating in abias-selectable sequential mode, there is usually one bump per pixel.For two-color sensors operating in a simultaneous mode, two or threebumps are required per pixel, making the fabrication very challenging.Prior art for two-color sensors are described in “Infrared Detectors forthe Future” by A. Rogalski, Acta Physica Polonica A pp 389, Vol 116, No3, (2009), which is incorporated herein by reference. FIGS. 1A, 1B, 1C,1D, 1E, 1F, 1G, 1H, 1I, 1J, 1K, and 1L, which are the same as shown inFIG. 7 of the Rogalski reference, show images and cross-section views ofprior art unit cells for various back-illuminated dual-band HgCdTedetector image sensors: FIGS. 1A and 1B a bias selectable n-p-nstructure, FIGS. 1C and 1D a simultaneous n-p-n design, FIGS. 1E and 1Fa simultaneous p-n-n-p, FIGS. 1G and 1H a simultaneous n-p-p-p-n design,FIGS. 1I and 1J a simultaneous structure based on p-on-n junctions, andFIGS. 1K and 1L a simultaneous structure based on n-on-p junctions.

The prior art requires either a contact made in a middle layer and anelectrical connection bridging from the middle layer to the top layer,or a dopant implantation step. These process can be complicated andhamper the ability to scale up simultaneous 2 color sensor arrays.

What is needed is an improved simultaneous dual-band image sensor, whichhas a simpler and higher yielding fabrication process. The embodimentsof the present disclosure answer these and other needs.

SUMMARY

In a first embodiment disclosed herein, a method of providing asimultaneous dual-band image sensor having a plurality of pixelscomprises providing a substrate, forming a common ground on thesubstrate, forming a Band 1 absorber layer on the common ground layer,forming a barrier layer on the Band 1 absorber layer, forming a Band 2absorber layer on the barrier layer, reticulating each pixel by etchingthe Band 2 absorber layer, the barrier layer and the Band 1 absorberlayer on sides of each pixel to but not through the common ground layer,etching a ring through the Band 2 absorber layer, and the barrier layerand into the Band 1 absorber layer but not through the Band 1 absorberlayer, forming a first contact on a portion of the Band 2 absorber layerinside the ring, and forming a second contact on a portion of the Band 2absorber layer outside the ring, wherein the Band 1 absorber layer isn-type and the Band 2 absorber layer is n-type, or wherein the Band 1absorber layer is p-type and the Band 2 absorber layer is p-type.

In another embodiment disclosed herein, a simultaneous dual-band imagesensor having a plurality of pixels comprises a substrate, a commonground on the substrate, wherein each pixel comprises a Band 1 absorberlayer on the common ground layer, a barrier layer on the Band 1 absorberlayer, a Band 2 absorber layer on the barrier layer, a ring opening inthe pixel formed by a removed portion of the Band 2 absorber layer, aremoved portion of the barrier layer and a removed portion of the Band 1absorber layer, wherein the ring opening does not extend through theBand 1 absorber layer, a first contact on a portion of the Band 2absorber layer inside the ring, and a second contact on a portion of theBand 2 absorber layer outside the ring, wherein the Band 1 absorberlayer is n-type and the Band 2 absorber layer is n-type, or wherein theBand 1 absorber layer is p-type and the Band 2 absorber layer is p-type.

In yet another embodiment disclosed herein, a method of providing asimultaneous dual-band image sensor having a plurality of pixelscomprises providing a substrate, forming a common ground on thesubstrate, forming a Band 1 diode layer on the common ground layer,forming a middle contact layer on the Band 1 diode layer, forming a Band2 diode layer on the middle contact layer, reticulating each pixel byetching the Band 2 diode layer, the middle contact layer and the Band 1diode layer on sides of each pixel to but not through the common groundlayer, etching a ring through the Band 2 diode layer, and the middlecontact layer and into the Band 1 diode layer but not through the Band 1diode layer, forming a first contact on a portion of the Band 2 diodelayer inside the ring, and forming a second contact on a portion of theBand 2 diode layer outside the ring, wherein the Band 1 diode layercomprises a first n-type layer on the common ground layer and a firstp-type layer on the first n-type layer, the Band 2 diode layer comprisesa second p-type layer on the middle contact layer and a second n-typelayer on the second p-type layer, and wherein forming a first contact ona portion of the Band 2 diode layer inside the ring and forming a secondcontact on a portion of the Band 2 diode layer outside the ringcomprises forming the first contact and the second contact on the secondn-type layer, or wherein the Band 1 diode layer comprises a first p-typelayer on the common ground layer and a first n-type layer on the firstp-type layer, the Band 2 diode layer comprises a second n-type layer onthe middle contact layer and a second p-type layer on the second n-typelayer, and wherein forming a first contact on a portion of the Band 2diode layer inside the ring and forming a second contact on a portion ofthe Band 2 diode layer outside the ring comprises forming the firstcontact and the second contact on the second p-type layer.

In still yet another embodiment disclosed herein, simultaneous dual-bandimage sensor having a plurality of pixels comprises a substrate, acommon ground on the substrate, wherein each pixel comprises a Band 1diode layer on the common ground layer, a middle contact layer on theBand 1 diode layer, a Band 2 diode layer on the middle contact layer, aring opening in the pixel formed by a removed portion of the Band 2diode layer, a removed portion of the middle contact layer and a removedportion of the Band 1 diode layer, wherein the ring opening does notextend through the Band 1 diode layer, a first contact on a portion ofthe Band 2 diode layer inside the ring, and a second contact on aportion of the Band 2 diode layer outside the ring, wherein the Band 1diode layer comprises a first n-type layer on the common ground layerand a first p-type layer on the first n-type layer, the Band 2 diodelayer comprises a second p-type layer on the middle contact layer and asecond n-type layer on the second p-type layer, and wherein the firstcontact and the second contact are on the second n-type layer, orwherein the Band 1 diode layer comprises a first p-type layer on thecommon ground layer and a first n-type layer on the first p-type layer,the Band 2 diode layer comprises a second n-type layer on the middlecontact layer and a second p-type layer on the second n-type layer, andwherein the first contact and the second contact are on the secondp-type layer.

These and other features and advantages will become further apparentfrom the detailed description and accompanying figures that follow. Inthe figures and description, numerals indicate the various features,like numerals referring to like features throughout both the drawingsand the description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, 1C, 1D, 1E, 1F, 1G, 1H, 1I, 1J, 1K and 1L show images andcross-section views of unit cells for various back-illuminated dual-bandHgCdTe detector image sensors: FIGS. 1A and 1B show a bias selectablen-p-n structure, FIGS. 1C and 1D show a simultaneous n-p-n design, FIGS.1E and 1F show a simultaneous p-n-n-p, FIGS. 1G and 1H show asimultaneous n-p-p-p-n design, FIGS. 1I and 1J show a simultaneousstructure based on p-on-n junctions, and FIGS. 1K and 1L show asimultaneous structure based on n-on-p junctions in accordance with theprior art.

FIG. 2A shows a representative structure layout for a prior artback-to-back diode architecture, and FIG. 2B shows a representativestructure layout for a prior art unipolar (nBn, pBp) architecture.

FIG. 3A shows a top view of a simultaneous two-color image sensordetector pixel in a two bump configuration in accordance with thepresent disclosure, and FIGS. 3C, 3D, 3E and 3F show side views ofdifferent configurations that may be used for the simultaneous two-colorimage sensor detector pixel of FIG. 3A. FIG. 3B shows an np-pnback-to-back dual-band image sensor, FIG. 3C shows a pn-np back-to-backdual-band image sensor, FIG. 3D shows an n-Barrier-n unipolar dual-bandimage sensor, and FIG. 3E shows a p-Barrier-p unipolar dual-band imagesensor in accordance with the present disclosure.

FIG. 4 shows a band structure diagram of the image sensor of FIG. 3Awith the configuration shown in 3D, the n-Barrier-n unipolar dual-bandimage sensor configuration, illustrating and validating the workingprinciple of simultaneous dual-band collection in accordance with thepresent disclosure.

FIGS. 5A and 5B show a top view and a side view schematic diagram of asimultaneous two-color image sensor detector with a configuration of onepixel for Band 1 and 4 sub-pixels for Band 2. FIG. 5B shows a sectionalside view using the unipolar architecture of FIG. 3D, however, the otherarchitectures shown in FIGS. 3B, 3C and 3E may also be used inaccordance with the present disclosure.

FIGS. 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 6I, 6J, 6K and 6L show a processflow for fabricating a dual-band image devices for 2 bump 2 colorconfiguration in accordance with the present disclosure.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toclearly describe various specific embodiments disclosed herein. Oneskilled in the art, however, will understand that the presently claimedinvention may be practiced without all of the specific details discussedbelow. In other instances, well known features have not been describedso as not to obscure the invention.

The present disclosure describes an image sensor device architecturethat enables fabrication of scalable simultaneous dual-band imagesensors with high yield. Specifically, the invention of the presentdisclosure allows for simultaneous collection of signals from twoelectromagnetic bands registered on the same pixel. This can be appliedfor a combination of any two electromagnetic spectral bands, such asinfrared, visible or ultra violet (UV). Compared to existingsimultaneous two-color technologies, the invention of the presentdisclosure has a simpler fabrication process and higher yields, whichallows scaling to larger image sensor sizes.

The present disclosure describes an image sensor architecture that iscompatible with both back-to-back diode architectures and unipolar (nBn,pBp) architectures. FIG. 2A shows a representative structure layout fora prior art back-to-back diode architecture, which may require a middlecontact, as shown. FIG. 2B shows a representative structure layout for aprior art unipolar (nBn, pBp) architecture.

FIG. 3A shows a top view of a simultaneous two-color image sensordetector pixel 10 with in a two bump configuration in accordance withthe present disclosure. The pixel has a bump 12 for a Band 1, and a bump14 for a Band 2. On the edge of the pixel is a common ground 16. A ring18 in the pixel separates the pixel into portion 20 inside the ring andportion 22 outside the ring. The ring is shown as circular, but can alsobe rectangular or polygonal in shape.

FIGS. 3B, 3C, 3D and 3E show side views of different configurations thatmay be used for the simultaneous two-color image sensor detector pixelof FIG. 3A.

FIG. 3B shows a np-pn back-to-back dual-band image sensor, FIG. 3C showsa pn-np back-to-back dual-band image sensor, FIG. 3D shown a n-Barrier-nunipolar dual-band image sensor, and FIG. 3E shows a p-Barrier-punipolar dual-band image sensor.

As shown in FIG. 3B, an np-pn back-to-back dual-band image sensor has acommon ground 16, which may be on a substrate 24, as shown in FIG. 6A.The Band 1 diode layer, shown in FIG. 3B is a p-n diode with the n-typelayer 30 on the common ground layer 16 and the p-type layer 32 on then-type layer 30. A middle contact layer 34 is on the p-type layer 32.The Band 2 diode layer, shown in FIG. 3B is a p-n diode with the p-typelayer 36 on the middle contact layer 34 and the n-type layer 38 on thep-type layer 36. As shown the ring 18 is formed by a removed portion ofthe Band 2 p-n diode 36, 38, the middle contact layer 34, and the p-typelayer 36 and into, but not through the n-type layer 30. The contact orbump 14 is on the Band 2 n-type layer 38 outside of the ring 18, and isbiased with a positive voltage. The contact or bump 12 is on the Band 2n-type layer 38 inside of the ring 18, and is biased with a negativevoltage.

As shown in FIG. 3C, a pn-np back-to-back dual-band image sensor has acommon ground 16, which may be on a substrate 24, as shown in FIG. 6A.The Band 1 diode layer, shown in FIG. 3C is a p-n diode with the p-typelayer 40 on the common ground layer 16 and the n-type layer 42 on thep-type layer 40. A middle contact layer 44 is on the n-type layer 42.The Band 2 diode layer, shown in FIG. 3C is a p-n diode with the n-typelayer 46 on the middle contact layer 44 and the p-type layer 48 on then-type layer 46. As shown the ring 18 is formed by a removed portion ofthe Band 2 p-n diode 48, 46, the middle contact layer 44, and the n-typelayer 42 and into, but not through the p-type layer 40. The contact orbump 14 is on the Band 2 p-type layer 48 outside of the ring 18, and isbiased with a negative voltage. The contact or bump 12 is on the Band 2p-type layer 48 inside of the ring 18, and is biased with a positivevoltage.

As shown in FIG. 3D, a n-barrier-n unipolar dual band image sensor has acommon ground 16, which may be on a substrate 24, as shown in FIG. 6A.The Band 1 absorber layer, shown in FIG. 3D is an n-type layer 50 on thecommon ground layer 16. A barrier layer 52 is on the n-type layer 50.The Band 2 absorber layer, shown in FIG. 3D is an n-type layer 54 on thebarrier layer 52. As shown the ring 18 is formed by a removed portion ofthe Band 2 n-type absorber 54, the barrier layer 52, and into, but notthrough the Band 1 n-type absorber layer 50. The contact or bump 14 ison the Band 2 n-type absorber layer 54 outside of the ring 18, and isbiased with a positive voltage. The contact or bump 12 is on the Band 2n-type absorber layer 54 inside of the ring 18, and is biased with anegative voltage.

As shown in FIG. 3E, a p-barrier-p unipolar dual band image sensor has acommon ground 16, which may be on a substrate 24, as shown in FIG. 6A.The Band 1 absorber layer, shown in FIG. 3D is a p-type layer 60 on thecommon ground layer 16. A barrier layer 62 is on the p-type layer 60.The Band 2 absorber layer, shown in FIG. 3E is a p-type layer 64 on thebarrier layer 62. As shown the ring 18 is formed by a removed portion ofthe Band 2 p-type absorber layer 64, the barrier layer 62, and into, butnot through the Band 1 p-type absorber layer 60. The contact or bump 14is on the Band 2 p-type absorber layer 64 outside of the ring 18, and isbiased with a negative voltage. The contact or bump 12 is on the Band 2p-type absorber layer 64 inside of the ring 18, and is biased with apositive voltage.

FIG. 4 shows a band structure diagram of the image sensor of FIG. 3Awith the configuration shown in 3D, the n-Barrier-n unipolar dual-bandimage sensor configuration, and illustrates and validates the workingprinciple of simultaneous dual-band collection. The common ground iskept at electrical neutral ground, while the Band 1 bump is biasednegatively and the Band 2 bump is bias positively. Photogenerated holesin Band 1 valence band, shown as blue circles in FIG. 4, can freely passthrough the Band 1 barrier to reach to the contact, creating a Band 1signal. Photogenerated holes in Band 2, shown as red circles in FIG. 4,also can freely pass through the Band 2 barrier to reach the commonground, generating a Band 2 signal. Both Band 1 and Band 2 can operateindependently, and simultaneously, thus producing simultaneous two colorimage sensing.

The device can also be operated in sub-pixel mode, where Band 1 has onepixel while Band 2 has multiple sub-pixels with individual contactbumps. FIGS. 5A illustrates an example where 4 sub-pixels of Band 2 areco-located with one superpixel of Band 1. The 4 sub-pixels areidentified as pixels 1, 2, 3, and 4, and are formed by separating thesubpixels by etching between the pixels, as shown by removed material 70in FIG. 5A. FIG. 5B shows a sectional side view through sub-pixels 1 and4 of Band 2 and superpixel 5 of Band 1 for the unipolar architecture ofFIG. 3D; however, the architectures of FIGS. 3B, 3C and 3E may also beused. The working principle is the same as illustrated in FIG. 4.

FIGS. 6A, 6B, 6C, 6D, 6E, 6F, 6G, 6H, 61, 6J, 6K and 6L show a processflow for fabricating a dual-band image sensor for a 2 bump 2 colorconfiguration. Alternating figures show a side view, such as FIG. 6A,and a corresponding top view, such as FIG. 6B, at each step. The processis illustrated for an n-Barrier-n unipolar dual band sensor, asillustrated in FIG. 3D, or a p-Barrier-p unipolar dual band sensor, asillustrated in FIG. 3E. The process for a np-pn back to back dual bandsensor, as illustrated in FIG. 3B, or a pn-np back to back dual bandsensor, as illustrated in FIG. 3C is similar, except that the as grownwafer in FIG. 6A needs to change to be in accordance with FIGS. 3B or3C.

In the step shown in FIGS. 6A and 6B a wafer is grown with layers of oneof the configurations of FIGS. 3B, 3C, 3D and 3E. FIGS. 6A and 6B showlayers grown for the n-Barrier-n unipolar dual band sensor of FIG. 3D,or the p-Barrier-p unipolar dual band sensor of FIG. 3E. A common groundlayer 16 is formed on a substrate 24. Then a Band 1 n-type layer orp-type absorber layer 80 is formed on the common ground layer 16. Then abarrier layer 82 is formed on the Band 1 layer. Then a Band 2 n-typelayer or p-type absorber layer 84 is formed on the barrier layer 82. Theas grown wafer of FIG. 6A may be large enough to accommodate manypixels.

Then, as shown in FIG. 6C and 6D, reticulation of the as grown wafer isperformed to separate the pixels on the as grown wafer. Pixelreticulation is performed by etching the sides of each pixel to thecommon ground layer 16, thereby separating each pixel while retainingthe common ground layer 16 for each pixel.

Next, a ring 18 is formed in the center of each pixel by etching a ring18 through the Band 2 absorber layer 84, the barrier layer 82 and intobut not through the Band 1 absorber layer 80 to create 2 regions of Band2 absorber materials: a Band 2 region inside the ring 86 and a Band 2region outside of the ring 88, as shown in FIGS. 6E and 6F.

Then, a passivation layer 90 is deposited over the pixel, as shown inFIGS. 6G and 6H.

Next, a first opening 92 in the passivation layer 90 is formed to exposethe Band 2 region inside the ring and a second opening 94 in thepassivation layer 90 is formed to expose the Band 2 region outside thering.

Then a first interconnect or contact 12, which may be a metal contact oran Indium bump, is formed in the first opening on the Band 2 regioninside the ring for signal collection of Band 1. Also a secondinterconnect or contact 14, which may be a metal contact or an Indiumbump, is formed in the second opening on the Band 2 region outside thering for signal collection of Band 2. The first interconnect or contactfor Band 1 collection is biased oppositely from the second interconnector contact for Band 2 collection, as shown in FIGS. 3B, 3C, 3D and 3E.Band 1 and Band 2 may be simultaneously collected.

The process for fabricating the 5 bump image sensor as shown in FIGS. 5Aand 5B is similar, and may include etching to remove the material 70, asshown in FIG. 5B to form the subpixels 1, 2, 3, 4 and 5 described above.It is expected that a person skilled in the art would understand how tofabricate a 5 bump image sensor as shown in FIGS. 5A and 5B for each ofthe configurations shown in FIGS. 3B, 3C, 3D and 3E.

Having now described the invention in accordance with the requirementsof the patent statutes, those skilled in this art will understand how tomake changes and modifications to the present invention to meet theirspecific requirements or conditions. Such changes and modifications maybe made without departing from the scope and spirit of the invention asdisclosed herein.

The foregoing Detailed Description of exemplary and preferredembodiments is presented for purposes of illustration and disclosure inaccordance with the requirements of the law. It is not intended to beexhaustive nor to limit the invention to the precise form(s) described,but only to enable others skilled in the art to understand how theinvention may be suited for a particular use or implementation. Thepossibility of modifications and variations will be apparent topractitioners skilled in the art. No limitation is intended by thedescription of exemplary embodiments which may have included tolerances,feature dimensions, specific operating conditions, engineeringspecifications, or the like, and which may vary between implementationsor with changes to the state of the art, and no limitation should beimplied therefrom. Applicant has made this disclosure with respect tothe current state of the art, but also contemplates advancements andthat adaptations in the future may take into consideration of thoseadvancements, namely in accordance with the then current state of theart. It is intended that the scope of the invention be defined by theClaims as written and equivalents as applicable. Reference to a claimelement in the singular is not intended to mean “one and only one”unless explicitly so stated. Moreover, no element, component, nor methodor process step in this disclosure is intended to be dedicated to thepublic regardless of whether the element, component, or step isexplicitly recited in the Claims. No claim element herein is to beconstrued under the provisions of 35 U.S.C. Sec. 112, sixth paragraph,unless the element is expressly recited using the phrase “means for . .. ” and no method or process step herein is to be construed under thoseprovisions unless the step, or steps, are expressly recited using thephrase “comprising the step(s) of . . . .”

1. A method of providing a simultaneous dual-band image sensor having aplurality of pixels comprising: providing a substrate; forming a commonground on the substrate; forming a Band 1 absorber layer on the commonground layer; forming a barrier layer on the Band 1 absorber layer;forming a Band 2 absorber layer on the barrier layer; reticulating eachpixel by etching the Band 2 absorber layer, the barrier layer and theBand 1 absorber layer on sides of each pixel to but not through thecommon ground layer; etching a ring through the Band 2 absorber layer,and the barrier layer and into the Band 1 absorber layer but not throughthe Band 1 absorber layer; forming a first contact on a portion of theBand 2 absorber layer inside the ring; and forming a second contact on aportion of the Band 2 absorber layer outside the ring; wherein the Band1 absorber layer is n-type and the Band 2 absorber layer is n-type; orwherein the Band 1 absorber layer is p-type and the Band 2 absorberlayer is p-type.
 2. The method of claim 1 further comprising: applying afirst bias voltage to the first contact; and applying a second biasvoltage to the second contact; wherein the first bias voltage isopposite in polarity to the second bias voltage.
 3. The method of claim1 wherein forming a first contact on a portion of the Band 2 absorberlayer inside the ring and forming a second contact on a portion of theBand 2 absorber layer outside the ring comprises: depositing apassivation layer; forming openings in the passivation layer; anddepositing contact material.
 4. The method of claim 1: wherein the firstcontact and the second contact comprise a bump.
 5. The method of claim1: wherein the ring has a circular, rectangular or polygonal shape. 6.The method of claim 1 wherein etching a ring through the Band 2 absorberlayer, and the barrier layer and into the Band 1 absorber layer but notthrough the Band 1 absorber layer further comprises; etching outside ofthe ring the Band 2 absorber layer, and the barrier layer and into theBand 1 absorber layer but not through the Band 1 absorber layer to forma plurality of subpixels outside of the ring; and forming a respectivecontact on each respective subpixel of the plurality of subpixels.7.-11. (canceled)
 12. A method of providing a simultaneous dual-bandimage sensor having a plurality of pixels comprising: providing asubstrate; forming a common ground on the substrate; forming a Band 1diode layer on the common ground layer; forming a middle contact layeron the Band 1 diode layer; forming a Band 2 diode layer on the middlecontact layer; reticulating each pixel by etching the Band 2 diodelayer, the middle contact layer and the Band 1 diode layer on sides ofeach pixel to but not through the common ground layer; etching a ringthrough the Band 2 diode layer, and the middle contact layer and intothe Band 1 diode layer but not through the Band 1 diode layer; forming afirst contact on a portion of the Band 2 diode layer inside the ring;and forming a second contact on a portion of the Band 2 diode layeroutside the ring; wherein the Band 1 diode layer comprises a firstn-type layer on the common ground layer and a first p-type layer on thefirst n-type layer, the Band 2 diode layer comprises a second p-typelayer on the middle contact layer and a second n-type layer on thesecond p-type layer, and wherein forming a first contact on a portion ofthe Band 2 diode layer inside the ring and forming a second contact on aportion of the Band 2 diode layer outside the ring comprises forming thefirst contact and the second contact on the second n-type layer; orwherein the Band 1 diode layer comprises a first p-type layer on thecommon ground layer and a first n-type layer on the first p-type layer,the Band 2 diode layer comprises a second n-type layer on the middlecontact layer and a second p-type layer on the second n-type layer, andwherein forming a first contact on a portion of the Band 2 diode layerinside the ring and forming a second contact on a portion of the Band 2diode layer outside the ring comprises forming the first contact and thesecond contact on the second p-type layer.
 13. The method of claim 12further comprising: applying a first bias voltage to the first contact;and applying a second bias voltage to the second contact; wherein thefirst bias voltage is opposite in polarity to the second bias voltage.14. The method of claim 12 wherein forming a first contact on a portionof the Band 2 diode layer inside the ring and forming a second contacton a portion of the Band 2 diode layer outside the ring comprises:depositing a passivation layer; forming openings in the passivationlayer; and depositing contact material.
 15. The method of claim 12:wherein the first contact and the second contact comprise a bump. 16.The method of claim 12: wherein the ring has a circular, rectangular orpolygonal shape.
 17. The method of claim 12 wherein etching a ringthrough the Band 2 diode layer, and the middle contact layer and intothe Band 1 diode layer but not through the Band 1 diode layer furthercomprises: etching outside of the ring the Band 2 diode layer, and themiddle contact layer and into the Band 1 diode layer but not through theBand 1 diode layer to form a plurality of subpixels outside of the ring;and forming a respective contact on each respective subpixel of theplurality of subpixels.
 18. A simultaneous dual-band image sensor havinga plurality of pixels comprising: a substrate; a common ground on thesubstrate; wherein each pixel comprises: a Band 1 diode layer on thecommon ground layer; a middle contact layer on the Band 1 diode layer; aBand 2 diode layer on the middle contact layer; a ring opening in thepixel formed by a removed portion of the Band 2 diode layer, a removedportion of the middle contact layer and a removed portion of the Band 1diode layer, wherein the ring opening does not extend through the Band 1diode layer; a first contact on a portion of the Band 2 diode layerinside the ring; and a second contact on a portion of the Band 2 diodelayer outside the ring; wherein the Band 1 diode layer comprises a firstn-type layer on the common ground layer and a first p-type layer on thefirst n-type layer, the Band 2 diode layer comprises a second p-typelayer on the middle contact layer and a second n-type layer on thesecond p-type layer, and wherein the first contact and the secondcontact are on the second n-type layer; or wherein the Band 1 diodelayer comprises a first p-type layer on the common ground layer and afirst n-type layer on the first p-type layer, the Band 2 diode layercomprises a second n-type layer on the middle contact layer and a secondp-type layer on the second n-type layer, and wherein the first contactand the second contact are on the second p-type layer.
 19. Thesimultaneous dual-band image sensor of claim 18 further comprising: thefirst contact having a first bias voltage; and the second contact havinga second bias voltage; wherein the first bias voltage is opposite inpolarity to the second bias voltage.
 20. The simultaneous dual-bandimage sensor of claim 18: wherein the first contact and the secondcontact comprise a bump.
 21. The simultaneous dual-band image sensor ofclaim 18: wherein the ring has a circular, rectangular or polygonalshape.
 22. The simultaneous dual-band image sensor of claim 18 furthercomprising: a plurality of subpixels outside of the ring formed byremoving a portion of the Band 2 diode layer, a portion of the middlecontact layer and a portion of the Band 1 diode layer, but not thoughthe Band 1 diode layer; and a respective contact on each respectivesubpixel of the plurality of subpixels.